The Queen's most senior adviser will deliver an "annual report" on the monarchy later this year as part of a package of modernising reforms that will also consider the issues of equal rights of succession for Catholics and women.

Sir Richard Luce, the Lord Chamberlain, will make the first public speech by the head of the Royal Household to reject claims that the monarchy is an outdated, irrelevant institution. The historic decision to end the Lord Chamberlain's silence was planned before the death of the Queen Mother but it will give Buckingham Palace a rare chance to put its own case at a time when polls have shown up to a third of the public backing a republic.

As part of the reforms, which have been sanctioned by the Queen, more duties will be switched to the Prince of Wales to develop a new role as "shadow king". The Prince will be given more access to government papers and take charge of more investitures and other functions normally carried out by the head of state.

The moves to increase his role will be overseen by Sir Michael Peat, who as Keeper of the Privy Purse led recent efforts to get across the message that the Royal Family keeps a tight rein on expenses. Sir Michael will become the Prince's private secretary this summer after he has finished organising the Queen's golden jubilee concerts at Buckingham Palace in June.

The monarch is also in favour of finally addressing the vexed constitutional issues of primogeniture – and a 300-year-old ban on Catholics becoming the sovereign. The 1701 Act of Settlement explicitly bars Roman Catholics from sitting on the throne or even marrying the monarch, while the ancient law of primogeniture gives sons precedence over elder sisters.

Both conventions have allowed republicans to portray the monarchy as anachronistic and out of touch with public opinion and any reform would be assured of speedy and strong support in Parliament. The Lord Chamberlain's annual speeches will explain how royal finances work and how the Queen sees her role both now and in the future.

The intention is to abandon the long-held tradition of Buckingham Palace refusing to comment on the speculation that constantly surrounds members of the Royal Family and to take a more proactive stance.

As part of the package of reforming measures, the public will be given more access to royal residences and art collections and more officials will give video interviews to be kept for posterity.